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GMATprep: all points (x,y) that lie below

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Re: GMATprep: all points (x,y) that lie below

by real2008 » Sun Jul 12, 2009 11:28 am
nhai2003 wrote:Please explain why the answer is E???? :shock:

OA: y<-1/2*x+3

But if x=5, y =2, 2<-1/2*5+3 => 2<0.5 doesn't make sense!
pl check your attached file....something wrong...
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Re: GMATprep: all points (x,y) that lie below

by nhai2003 » Sun Jul 12, 2009 2:04 pm
real2008 wrote:
nhai2003 wrote:Please explain why the answer is E???? :shock:

OA: y<-1/2*x+3

But if x=5, y =2, 2<-1/2*5+3 => 2<0.5 doesn't make sense!
pl check your attached file....something wrong...
Thanks I have attached new file

Guys Please Help Me!
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by shibal » Sun Jul 12, 2009 2:08 pm
sets below the line.... therefore (5,2) can't be used... try for example (-5,-1) and u'll see that only option E
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by nhai2003 » Sun Jul 12, 2009 3:10 pm
shibal wrote:sets below the line.... therefore (5,2) can't be used... try for example (-5,-1) and u'll see that only option E
why set (5,2) can't be used? It said se (x,y) below the line (6,3)
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by shibal » Sun Jul 12, 2009 3:17 pm
draw the coordinate system and the line, and then point out 5,2.... u'll see the point is above the line....
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by real2008 » Sun Jul 12, 2009 10:29 pm
from the graph you may find x axis intercept is (a) 6 and for Y axis (b) is 3.

If these two intercepts are known, the eqn can be written in this form

x/a + y/b = 1

Now,

x/6 + y/3 = 1

rearranging,

y= 3- x/2 (first form)

x+2y-6=0 (second form)

now as the mentioned point lies below the line , i.e. to the side where origin also lies, then the expression x+2y-6 for a point lying below the line [say (1,1)] will have same polarity as the expression for (0,0) has.

so for (0,0) the expression x+2y-6= -6
[for (1,1) the expression x+2y-6= -3]

that means x+2y-6<0
or, 2y<6-x

or, y<3-x/2

i.e choice E

HTH
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